Process_item not updating EKPO ME21N : S4hana

I have added custom fields using CMOD at item level in me21n , Based on custom fields value i have to change field weunb value to X in ekpo , i have used BADI method PROCESS_ITEM , it is transferring X to weunb , but it is triggering when user press enter at item level .

in a case if user press SAVE button directly , it is not getting triggered if it is a custom tab.